What Is Surface RA?


Surface RA stands for “Roughness Average” and is a parameter used to measure the surface texture of a material. According to the British Stainless Steel Association, there are over 100 ways to measure the surface of a material, but RA is one of the simplest and most effective.

Surface Texture

The surface of materials such as stainless steel, which are typically machined, ground or polished, consists of a series of peaks and troughs caused by the finishing processes. These imperfections can affect the strength and performance of machined components.


RA is calculated by measuring the average length between peaks and troughs on the surface of a material and their deviation from a mean or center line. Extreme peaks and troughs are discarded and do not affect the overall calculation. For these reasons, RA is also known as CLA or “Center Line Average.”


RA is commonly used in industry to monitor mechanical production processes, such as grinding. It is a particularly useful parameter for measuring consistency of surface texture in situation where cutting tips, speeds and lubricants are, or at least should be, the same at all times.

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